From: Date: March 17 2003 4:47am
Subject: Re: Foreign Key and default action/RESTRICT behaviour?
List-Archive: http://lists.mysql.com/mysql/134863
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At 4:13 +0100 3/17/03, Andreas wrote:
>>>RESTRICT is, of course, the default 'action'. ON DELETE and ON UPDATE are
>>>later additions.
>>
>Paul DuBois wrote:
>>I see in the change notes that ON UPDATE was implemented in 4.0.8.
>>
>>But how can ON DELETE be a later addition than RESTRICT?  I was under the
>>impression that RESTRICT wasn't even implemented.
>>
>>Also, the manual lists SET DEFAULT as a reference option for the general
>>CREATE TABLE syntax.  Does that come into play for InnoDB at all?
>
>As I get it, RESTRICT is no real "action" at all, since all it does 
>is watching the foreign key restriction to be followed.

That's an action in the sense that it prevents a parent table record
from being deleted.

>
>ON DELETE was implemented because it makes sense and is actually 
>useful to safe some work.

What I meant is that because RESTRICT is one of the options for the
ON DELETE clause, you cannot implement RESTRICT *before* ON DELETE.
You cannot implement an option before the clause that it is an option *of*.

It makes sense to say that ON UPDATE was updated after ON DELETE, because
it was.

>ON UPDATE seams to me to be more exotic since most foreign keys have 
>a primary key on one side, so the update target is a primary key, 
>which is not really elegant in my view.
>
>Both actions DELETE and UPDATE have drawbacks if you have some 
>relations not covered by an explicit foreign-key-rule or if some 
>tables are still myisam.
>
>Anyway RESTRICT is the core funtionality of foreign keys. Without it 
>FKs don't make much sense at all.
>
>
>sql, query yada yada ...


-- 
Paul DuBois
http://www.kitebird.com/
sql, query